We calculate these odds ratios for all 10 events in GWTC-1 [1]}, and plot the results in Fig. REF .
For GW170729—the event with the most massive primary black hole—we favor a 1G+1G  over a 1G+2G  origin with 25:1 odds when including the zero-spin formation channel.
The probability that GW170729 is of hierarchical origin (either 1G+2G  or 2G+2G ) is \(4\%\) .
GW151226, which has the most confidently measured non-zero spin [2]}, [1]}, [4]}—we find that \(\log _{10} (Z_\chi /Z_0) = 6.5\) —has the second highest probability (\(0.2\%\) ) for a hierarchical origin.
Across all 10 systems in GWTC-1, we find the probability that at least one binary black hole system is of hierarchical origin is \(5\%\) .
